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Conversion of internal gravity waves into magnetic waves

Lecoanet, D. and Vasil, G. M. and Fuller, J. and Cantiello, M. and Burns, K. J. (2017) Conversion of internal gravity waves into magnetic waves. Monthly Notices of the Royal Astronomical Society, 466 (2). pp. 2181-2193. ISSN 0035-8711. https://resolver.caltech.edu/CaltechAUTHORS:20190425-152212282

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Abstract

Asteroseismology probes the interiors of stars by studying oscillation modes at a star's surface. Although pulsation spectra are well understood for solar-like oscillators, a substantial fraction of red giant stars observed by Kepler exhibit abnormally low-amplitude dipole oscillation modes. Fuller et al. (2015) suggest this effect is produced by strong core magnetic fields that scatter dipole internal gravity waves (IGWs) into higher multipole IGWs or magnetic waves. In this paper, we study the interaction of IGWs with a magnetic field to test this mechanism. We consider two background stellar structures: one with a uniform magnetic field, and another with a magnetic field that varies both horizontally and vertically. We derive analytic solutions to the wave propagation problem and validate them with numerical simulations. In both cases, we find perfect conversion from IGWs into magnetic waves when the IGWs propagate into a region exceeding a critical magnetic field strength. Downward propagating IGWs cannot reflect into upward propagating IGWs because their vertical wavenumber never approaches zero. Instead, they are converted into upward propagating slow (Alfvénic) waves, and we show they will likely dissipate as they propagate back into weakly magnetized regions. Therefore, strong internal magnetic fields can produce dipole mode suppression in red giants, and gravity modes will likely be totally absent from the pulsation spectra of sufficiently magnetized stars.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1093/mnras/stw3273DOIArticle
https://arxiv.org/abs/1610.08506arXivDiscussion Paper
ORCID:
AuthorORCID
Fuller, J.0000-0002-4544-0750
Additional Information:© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 December 13. Received 2016 December 12; in original form 2016 October 18. The authors would like to thank Lars Bildsten, Eliot Quataert, Ellen Zweibel, Anna Lieb, Stephane Mathis, Dennis Stello, Rafael Garcia and Frank Timmes for helpful discussions. DL is supported by the Hertz Foundation, a PCTS fellowship, and a Lyman Spitzer Jr fellowship, and would like to thank the University of Sydney School of Mathematics and Statistics for helping fund a visit to Sydney. This work has been carried out in the framework of the Labex MEC (ANR-10-LABX-0092) and of the A*MIDEX project (ANR-11-IDEX-0001-02), funded by the ‘Investissements d'Avenir’ French Government programme managed by the French National Research Agency (ANR). GMV acknowledges support from the Australian Research Council, project number DE140101960. This research is funded in part by the Gordon and Betty Moore Foundation through Grant GBMF5076 to Lars Bildsten, Eliot Quataert and E. Sterl Phinney. This research was supported in part by the National Science Foundation under Grant No. NSF PHY-1125915. The authors thank KITP for supporting a follow-up meeting where much of this work was initiated. Resources supporting this work were provided by the NASA High-End Computing (HEC) Programme through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. This project was supported by NASA under the SPIDER TCAN, grant number NNX14AB53G.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funders:
Funding AgencyGrant Number
Fannie and John Hertz FoundationUNSPECIFIED
Princeton UniversityUNSPECIFIED
University of SydneyUNSPECIFIED
Agence Nationale pour la Recherche (ANR)ANR-10-LABX-0092
Agence Nationale pour la Recherche (ANR)ANR-11-IDEX-0001-02
Australian Research CouncilDE140101960
Gordon and Betty Moore FoundationGBMF5076
NSFPHY-1125915
Kavli Institute for Theoretical PhysicsUNSPECIFIED
NASANNX14AB53G
Subject Keywords:asteroseismology, scattering, waves, stars: magnetic field
Issue or Number:2
Record Number:CaltechAUTHORS:20190425-152212282
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190425-152212282
Official Citation:D. Lecoanet, G. M. Vasil, J. Fuller, M. Cantiello, K. J. Burns, Conversion of internal gravity waves into magnetic waves, Monthly Notices of the Royal Astronomical Society, Volume 466, Issue 2, April 2017, Pages 2181–2193, https://doi.org/10.1093/mnras/stw3273
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94983
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:26 Apr 2019 16:25
Last Modified:03 Oct 2019 21:09

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